IOS 10 has been very buggy. I experience the above issue regularly and another which I haven't seen documented. The phone soft boots every now and again. I get the black screen with spinning gear, it goes dark and about 10 seconds later I am back at the lock screen. It appears to me to be a reboot, but I don't know how to determine the last boot time to confirm this. I thought I might have a hardware issue, but this problem did not occur prior to upgrading to IOS 10.